This is what should be fitted to all 335 BMW's but is not.
BMW chose to save money by adding an open diff arrangement, as the cars are now electronically controlled to prevent slides and wheel spin via DTC/DSC "nanny aids". These "nanny aids" sense when the wheels are spinning or sliding and for the sake of stability, individually brakes the wheels via the ABS System and the other limits engine torque via the ECU till traction is re-established.....way to go BMW

What you're looking at above by the lucky bast..d, is the aftermarket Quaife ATB differential unit which sits inside the 335's diff housing and replaces the open diff . It's basically a LSD (limited slip diff) but has special features like torque biasing. These units have no clutch plates that wear out over time but incorporate gearing to adjust the torque delivery to the rear wheel that needs it most - the one not spinning. The rear wheel that is spinning will have it's torque reduced .......hello controllable powerslides.. aka drifting !!

Read this from Birds for a description:
" Quite simply, it increases the torque presented at the tyre contact patch
with the road, which increases the force exerted on the road, and, as Mr
Newton states, this increases the rate of acceleration. In the situation
where one wheel is spinning, a car with an "open" diff can potentially lose
all drive. This ATB diff prevents the wheel with the least grip from spinning,
traction control is therefore not triggered anywhere near as often, and the
car accelerates to its true potential ".

I guess I now need to book myself on another skid pan day to learn how it affects things & more importantly how to utilize it at the edge.

Awesome mod WOPALX, if I had a 335 it would be my first for sure! LSD+RWD is just so much fun it should be illegal...In fact it probably is.

Just take baby steps, give it one big stab of throttle mid corner, let the car rotate around the front wheels, lift off, feel it...Don't give the throttle a second press until you are comfortable with this initial feeling.